Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
Hi full - Maybe (item, full) Hrm, what exactly is the return data here? Is is the head and the tail if the list has = 1 item, or Nothing otherwise? Or...? Yes, its the projection onto another type: [] = Nothing (x:xs) = Just (x, xs) What is the problem with MPTC in base? MPTC is not a part of any Haskell standard. The rules surrounding MPTC are not clear. People want to remove MPTC's/functional dependencies, or modify them with associated types. Compilers such as nhc and yhc can't implement them. Once they are in Haskell', with an associated set of restrictions/overlap rules etc, then they can be freely used with the base library. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
John Goerzen wrote: On 2008-02-20, John Goerzen [EMAIL PROTECTED] wrote: I notice that Data.Foldable does some similar things but does not use multi-parameter type classes. I seem to recall that I attempted to do this in the same manner, but got tripped up somewhere. I can't remember now exactly what the problem was, but I can go back and look if nobody knows off-hand. I went back and looked. The problem is that ByteString doesn't work as a member of Foldable, or of ListLike without it being MPTC. Trying to do so yields: ListLike.hs:217:20: Kind mis-match Expected kind `* - *', but `BS.ByteString' has kind `*' In the instance declaration for `F.Foldable BS.ByteString' Is there any way around that, other than MPTC? Not directly, no. The point about Foldable, Functor, and Monad, is that they enforce the connection between container and contents. If the contents is of type a, the container is of type f a for a fixed type constructor 'f'. This works for [], Seq, and so on, but fails for ByteString. To go to the next level, for ByteString you either need type-level functions (to generalise 'f' from type constructor to arbitrary function :: * - *), or MPTCs (to make the association between container and contents explicit). However, passing around dictionaries is certainly a solution which works in haskell98. I haven't thought it through enough to see if it would be unpleasantly verbose in practice. Jules ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
On Feb 20, 2008 12:48 PM, Chad Scherrer [EMAIL PROTECTED] wrote: StorableVector should fill this gap. http://code.haskell.org/~sjanssen/storablevector/ Yes, it could, but (1) it's way behind ByteString in terms of optimizations (== fusion) (2) there's (as far as I know) not a StorableVector.Lazy, which is very much needed To catch up on both fronts, we're looking at a lot of duplicate code. For anyone looking into it - the StorableVector fusion would have to be quite different from the current ByteString fusion framework. Maybe it would be enough to lay down a Stream fusion framework for StorableVectors. -Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
On Feb 20, 2008 10:57 AM, Antoine Latter [EMAIL PROTECTED] wrote: For anyone looking into it - the StorableVector fusion would have to be quite different from the current ByteString fusion framework. Maybe it would be enough to lay down a Stream fusion framework for StorableVectors. I must be missing something. Why would it have to be so different? Chad ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
On Feb 20, 2008 12:59 PM, Chad Scherrer [EMAIL PROTECTED] wrote: On Feb 20, 2008 10:57 AM, Antoine Latter [EMAIL PROTECTED] wrote: For anyone looking into it - the StorableVector fusion would have to be quite different from the current ByteString fusion framework. Maybe it would be enough to lay down a Stream fusion framework for StorableVectors. I must be missing something. Why would it have to be so different? From what I saw of Data.ByteString.Fusion, it relies on the assumption that the elements of the output array are of the same size and alignment as the elements of all of the arrays in the fused intermediate steps. That way, all of the intermediate stages can mutate the output array in place. This works because all of the fusable bytestring functions have types along the lines of: map :: (Word8 - Word8) - ByteString - ByteString With StorableVector, it'd be nice to support the fusion of: map :: (a - b) - Vector a - Vector b All of this just comes from me reading the code, so I could be miss-interpreting something. The NDP papers probably have something interesting to say about this, but I haven't taken the time to try and understand/simplify what they do. -Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
Antoine Latter [EMAIL PROTECTED] wrote: From what I saw of Data.ByteString.Fusion, it relies on the assumption that the elements of the output array are of the same size and alignment as the elements of all of the arrays in the fused intermediate steps. That way, all of the intermediate stages can mutate the output array in place. I see a lot in there involving the elimination of intermediate data structures, but nothing about destructive updates. The API is purely functional, and what you're talking about would need to be done in the IO monad to be sure you don't throw away stuff you might need to use again. Chad ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
On Wed, Feb 20, 2008 at 11:18:51PM +0100, Ben Franksen wrote: John Goerzen wrote: On 2008-02-20, Jules Bean [EMAIL PROTECTED] wrote: Not directly, no. The point about Foldable, Functor, and Monad, is that they enforce the connection between container and contents. If the contents is of type a, the container is of type f a for a fixed type constructor 'f'. This works for [], Seq, and so on, but fails for ByteString. Right. In a pure abstract sense, we humans know there is a relationship between container and contents: a ByteString always contains a Word8 (or a Char8 if we choose the alternative implementation). But that is not expressed in the type of ByteString. Hm, making a function out of a constant is easy on the value level, just use (const x) instead of (x). So, what about wrapping ByteString in a GADT, like this data ByteString' a where BS' :: Word8 - ByteString' Word8 ? I probably overlooked something important here... The problem is that while this would change the kind of ByteString to the same as the kind expected by Functor, you still couldn't define a proper Functor instance, since only ByteString' Word8 can ever actually be created. i.e. how could you implement fmapBS :: (a - b) - ByteString' a - ByteString' b -- David Roundy Department of Physics Oregon State University ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
G'day all. Quoting Neil Mitchell [EMAIL PROTECTED]: Yes, its the projection onto another type: [] = Nothing (x:xs) = Just (x, xs) Also known as msplit: http://www.haskell.org/haskellwiki/New_monads/MonadSplit Cheers, Andrew Bromage ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The Proliferation of List-Like Types
On Wed, Feb 20, 2008 at 10:46 PM, [EMAIL PROTECTED] wrote: Quoting Neil Mitchell [EMAIL PROTECTED]: Yes, its the projection onto another type: [] = Nothing (x:xs) = Just (x, xs) Also known as msplit: http://www.haskell.org/haskellwiki/New_monads/MonadSplit Almost. The projection has type f a - Maybe (a, f a), but msplit has type f a - f (Maybe (a, f a)). -- Dave Menendez [EMAIL PROTECTED] http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
